As a kind of pipe joint, there is known a slip-on type pipe joint. The slip-on type pipe joint is arranged so that a socket and a spigot can be jointed by placing a sealing material around the inner circumference of the socket and then inserting the spigot into the socket while pressing the sealing material. A slip-on type pipe joint has recently been proposed which is given a function of preventing a joint separation.
In such a slip-on type pipe joint, a ridge formed around the outer circumference of the end of a spigot of a cast iron pipe engages with a lock ring received in the inner circumference of a socket to prevent a joint separation. When the ridge around the end of the spigot is formed, an annular groove is formed around the outer circumference of the end of the spigot, in which groove a separation-preventing ring is secured. The ring is made of steel, high tensile cast iron such as ductile cast iron, or the like.
For a known ridge, a ring having a slit on its circumference is generally fitted into a groove formed in the outer surface of a spigot and then secured by welding.
The known art has a problem that the ridge formation is laborious because the outer surface of a spigot needs be formed with a groove.